Imagine you have 10 “Click” events.
You want to change them all to be “Simulate Click” and change them all from “Left Click” to Right-Clicks. You don’t have to do that 10 times in a row!
Just pick one click Activitiy, then hold Ctrl and left click on each other Activity.
As you select more activities, the Properties list will shrink to only contain the things that each selected item has in common.
If you make changes to any property now, every selected activity will be updated at once.